The present invention relates to semiconductor devices. For example, the present invention can be preferably applied to an optical-coupling type isolation amplifier used for transmitting and receiving optical signals.
Manufacturing instruments such as AC motors and inverters are widely used in the state of being controlled by control devices in factories and plants. There are many cases where electric power sources used for these manufacturing instruments are required to have high voltages. On the other hand, the control devices that give control signals to these instruments do not require electric power sources with high voltages. In other words, the control devices have only to be supplied with electric power sources whose voltage values are large enough to activate logic circuits the control devices include.
An optical-coupling type isolation amplifier, which has some regions of different voltages isolated from each other and transmits control signals, is used to materialize such control devices. The optical-coupling type isolation amplifier includes an input side (primary) circuit that receives a signal from a transmitter, and an output side (secondary) circuit that outputs a signal to a receiver.
The input side circuit includes an A/D (Analog to Digital) converter (for example, a delta-sigma AD converter), an encoder that encodes a signal sent from the transmitter, a driver that drives a light-emitting diode (LED), and the like. The output side circuit includes an optical receiver circuit that receives light emitted by the light-emitting diode, a decoder that decodes the signal encoded by the input side circuit, and the like.
In the optical-coupling type isolation amplifier, an optical signal is transmitted between the light-emitting diode and a photo diode by using a pulse-width modulated clock pulse for the signal transmission between the input side circuit and the output side circuit, so that both isolation and high-accurate signal transmission are realized.
As related technologies, Japanese Unexamined Patent Application Publications No. 2004-179982, No. 2008-236392, No. 2010-178327, and No. 2007-096593 disclose technologies which reduce pulse-width distortion generated in the output signals of optical-coupling type isolation amplifiers. In addition, Japanese Unexamined Patent Application Publication No. 2006-340072 discloses an optical-coupling type isolation amplifier that has improved noise tolerance.